Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
1
FIRE AND BIRDS IN THE SOUTHWESTERN UNITED STATES
CARL E. BOCK AND WILLIAM M. BLOCK
Abstract. Fire is an important ecological force in many southwestern ecosystems, but frequencies, sizes,
and intensities of fi re have been altered historically by grazing, logging, exotic vegetation, and suppression.
Prescribed burning should be applied widely, but under experimental conditions that facilitate studying its
impacts on birds and other components of biodiversity. Exceptions are Sonoran, Mojave, and Chihuahuan
desert scrub, and riparian woodlands, where the increased fuel loads caused by invasions of exotic grasses
and trees have increased the frequency and intensity of wildfi res that now are generally destructive to native
vegetation. Fire once played a critical role in maintaining a balance between herbaceous and woody vegetation
in desert grasslands, and in providing a short-term stimulus to forb and seed production. A 3–5 yr fi re-return
interval likely will sustain most desert grassland birds, but large areas should remain unburned to serve spe-
cies dependent upon woody vegetation. Understory fi re once maintained relatively open oak savanna, pinyon-
juniper, pine-oak, ponderosa pine (Pinus ponderosa), and low elevation mixed-conifer forests and their bird
assemblages, but current fuel conditions are more likely to result in stand-replacement fi res outside the range
of natural variation. Prescribed burning, thinning, and grazing management will be needed to return fi re to its
prehistoric role in these habitats. Fire also should be applied in high elevation mixed-conifer forests, especially
to increase aspen stands that are important for many birds, but this will be an especially diffi cult challenge in
an ecosystem where stand-replacement fi res are natural events. Overall, surprisingly little is known about avian
responses to southwestern fi res, except as can be inferred from fi re effects on vegetation. We call for coopera-
tion between managers and researchers to replicate burns in appropriate habitats that will permit rigorous study
of community and population-demographic responses of breeding, migrating, and wintering birds. This research
is critical and urgent, given the present threat to many southwestern ecosystems from destructive wildfi res, and
the need to develop fi re management strategies that not only reduce risk but also sustain bird populations and
other components of southwestern biological diversity.
Key words: birds, chaparral, desert, fi re, grassland, mixed-conifer, pine-oak, prescribed burning, riparian,
savanna, Southwest, wildfi re.
FUEGO Y AVES EN EL SUROESTE DE ESTADOS UNIDOSResumen. El fuego es una fuerza ecológica importante en varios ecosistemas sur-occidentales, pero sus fre-
cuencias, tamaños e intensidades han sido alteradas históricamente por el pastoreo, aprovechamientos fores-
tales, vegetación exótica y supresión. Las quemas prescritas deberían ser aplicadas, pero bajo condiciones
experimentales las cuales faciliten el estudio de sus impactos en aves y otros componentes de biodiversidad.
Algunas excepciones son el matorral xerófi lo de Sonora, Mojave y Chihuahua, y bosques de galería, donde el
incremento del material combustible causado por invasiones de pastos y árboles exóticos ha incrementado la
frecuencia e intensidad de incendios, los cuales generalmente son dañinos para la vegetación nativa. Alguna vez
el fuego jugó un papel importante para mantener el balance entre la vegetación herbácea y forestal en pastizales
del desierto, así como para estimular el retoño y la producción de semilla en el corto plazo. Una repetición
de incendio con intervalos de 4–5 años, sustentaría a la mayoría de las aves de pastizales, pero grandes áreas
deberían permanecer sin incendiarse para servir a las especies dependientes de la vegetación forestal. El fuego
algún tiempo mantuvo relativamente abierta la sabana de encinos, piñón-juníperos, pino-encino, pino ponderosa
(Pinus ponderosa), y bosques de coníferas mixtos de bajas elevaciones, así como sus aves correspondientes,
pero las condiciones actuales de combustible tienden mas a resultar en reemplazos del crecimiento de plantas
fuera del rango natural de variación. Se requerirían quemas preescritas, aclareos y el manejo de pastizales para
regresar al papel que jugaba el fuego en la prehistoria en estos habitats. El fuego también debería ser aplicado en
bosques de coníferas mixtos de alta elevación, especialmente para incrementar el crecimiento de aspen, el cual
es importante para varias aves, pero esto sería un reto sumamente importante en ecosistemas donde el reemplazo
del crecimiento de plantas en incendios es un evento natural. Es sorprendente lo poco que se conoce acerca de
las respuestas de las aves a los incendios sur-occidentales, a excepción en lo que se refi ere a la respuesta de la
vegetación al fuego. Pedimos cooperación entre los manejadores e investigadores para replicar incendios en
habitats apropiados, que permitan rigurosos estudios de respuestas demográfi cas de comunidades y poblaciones,
de aves reproductoras, migratorias y aves que permanecen en estas regiones durante el invierno. Este estudio
es crítico y urgente, dado el presente peligro que varios ecosistemas sur-occidentales enfrentan debido a incen-
Studies in Avian Biology No. 30:1–XXX
STUDIES IN AVIAN BIOLOGY2 NO. 30
The conditions necessary and suffi cient for fi re
in natural ecosystems include a source of ignition,
such as lightning or anthropogenic burning, and an
adequate quantity of dry fuel (Pyne et al. 1996).
These conditions are met in most ecosystems of
the southwestern United States (McPherson and
Weltzin 2000), and the ecological importance
of fi re in the region has long been recognized
(Leopold 1924, Humphrey 1958). We also know
that humans have drastically altered historic fre-
quencies, sizes, and intensities of fi re by anthro-
pogenic disturbances such as logging, livestock
grazing, introduction of exotics, landscape frag-
mentation, and suppression efforts (Covington and
Moore 1994, Bahre 1985, 1995, McPherson 1995,
Moir et al. 1997). In 1988 and again in 1996, groups
of researchers and managers assembled to synthe-
size the known effects of fi re on natural resources in
the southwestern United States, including its plant
communities and wildlife, and to recommend ways
to respond to wildfi re and to use prescribed burning
(Krammes 1990, Ffolliott et al. 1996). This paper is
a follow-up to the results of those conferences, with
a specifi c emphasis on populations and communi-
ties of southwestern birds.
For purposes of this review, we defi ne the
Southwest as that portion of the United States
adjacent to Mexico, from the Mojave desert of
southern Nevada and southeastern California east-
ward across Arizona and New Mexico and into
trans-Pecos Texas (Fig. 1). Our defi nitions and
descriptions of major ecosystems in the Southwest
are taken largely from Brown (1982a) and Barbour
and Billings (2000). We consider eight major
ecosystems in this review: (1) Chihuahuan desert
and associated desert grasslands, (2) Sonoran and
Mojave deserts, (3) Madrean evergreen savanna,
(4) interior chaparral, (5) pinyon-juniper woodland,
(6) pine and pine-oak woodland, (7) mixed-coni-
fer forest, and (8) riparian woodlands. For each
of these ecosystems we describe the distribution,
elevation, size, major vegetation, and character-
istic birds, including those identifi ed as priority
species (Partners in Flight 2004). We describe the
prehistoric importance of fi re, fi re-return interval,
and its effects on vegetation. We then review how
prehistoric fi re regimes have been altered by recent
human activities. We discuss known and probable
effects of fi re on birds under present conditions.
At the end of each section, we suggest how both
wild and prescribed fi re should be managed for the
benefi t of birds, and identify the major unanswered
questions and research priorities regarding the
impact of fi re on avian communities.
CHIHUAHUAN DESERT SCRUB AND DESERT
GRASSLANDS
The Chihuahuan desert includes more than
45,000,000 ha, distributed mostly between 1,000 and
2,000 m elevation, from the Valley of Mexico north
into Trans-Pecos Texas, southern New Mexico, and
extreme southeastern Arizona (MacMahon 2000).
Desert grassland (about 50,000,000 ha) generally
surrounds the Chihuahuan Desert, forming a patchy
belt that grades from desert scrub up into Madrean
evergreen woodland, pinyon-juniper woodland, and
pine-oak woodland from Mexico City north to the
southwestern United States (McClaran 1995). We
consider these ecosystems together because they
are similar in vegetation (Axelrod 1985, Burgess
1995, MacMahon 2000, McLaughlin et al. 2001),
they interdigitate on a fi ne geographic scale (Lowe
and Brown 1982), and desert scrub has replaced
large areas of southwestern grasslands within his-
toric time, due at least in part to altered fi re regimes
(Humphrey 1974, McPherson 1995, Whitford 2002,
Turner et al. 2003).
Dominant vegetation of the Chihuahuan desert
includes shrubs and small trees, especially creosote-
bush (Larrea tridentata), tarbush (Flourensia cer-
nua), mesquite (Prosopis spp.), and acacia (Acacia
spp.), along with various species of Yucca and
Agave (Brown 1982a, MacMahon 2000, Whitford
2002). Each of these plants extends into desert
grasslands as well, along with smaller shrubs such
as burroweed (Isocoma tenuisecta) and various spe-
cies of Baccharis (McClaran 1995). Black grama
(Bouteloua eriopoda) and tobosa (Hilaria mutica)
are predominant grasses of the Chihuahuan desert,
and these also extend into desert grasslands where
they mix with a variety of warm-season peren-
nial bunchgrasses, especially those in the genera
Bouteloua, Eragrostis, and Aristida (McClaran
1995, McLaughlin et al. 2001).
Characteristic birds of desert grassland and
Chihuahuan desert include species with a spectrum of
habitat requirements, from those associated primar-
dios destructivos, así como por la necesidad de desarrollar estrategias de manejo las cuales no solo disminuyan
el riesgo, sino también sustenten las poblaciones de aves y otros componentes de diversidad biológica de los
ecosistemas sur-occidentales.
SOUTHWESTERN UNITED STATES—Bock and Block 3
ily with shrubs, such as Gambel’s Quail (Callipepla
gambelii) and Cactus Wren (Campylrorhynchus
brunneicapillus), to those associated with relatively
open grasslands, such as Horned Lark (Eremophila
alpestris) and Grasshopper Sparrow (Ammodramus
savannarum) (Brown 1982a). Desert grasslands
are particularly important wintering habitat for a
number of migratory sparrows, because of their seed
production (Pulliam and Dunning 1987). Given his-
toric conversions of grassland to desert scrub, it is
not surprising that many Partners in Flight priority
species for this region are associated with grass-
lands, or at least with areas that include signifi cant
grass cover. Examples include Ferruginous Hawk
(Buteo regalis), Aplomado Falcon (Falco femora-
lis), Sprague’s Pipit (Anthus spragueii), Cassin’s
Sparrow (Aimophila cassinii), Botteri’s Sparrow
(Aimophila botterii), Grasshopper Sparrow, and
Baird’s Sparrow (Ammodramus bairdii), and two
birds restricted to grasslands of Arizona and Sonora,
the endangered Masked Bobwhite (Colinus virgin-
ianus ridgwayi), and the Rufous-winged Sparrow
(Aimophila carpalis).
FIRE IN CHIHUAHUAN DESERT SCRUB AND DESERT
GRASSLANDS
Fires probably were very uncommon in
Chihuahuan desert proper, and its dominant grass,
black grama (Bouteloua eriopoda), is damaged by
fi re (Gosz and Gosz 1996). However, fi res probably
occurred once every 7–10 yr in higher, cooler, and
wetter desert grasslands above the fringes of the
Chihuahuan desert, and prehistoric fi re served to
keep these areas relatively free of trees and shrubs
(McPherson 1995, McPherson and Weltzin 2000).
Southwestern grasslands from west Texas to
southeastern Arizona almost universally experienced
major invasions of woody plants over the course of
the twentieth century (Buffi ngton and Herbel 1965,
Bahre and Shelton 1993, Archer 1994). These events
have been attributed to climate change, livestock
grazing, prairie dog (Cynomys spp.) control, and fi re
exclusion resulting from suppression efforts and loss
of fi ne fuels to domestic grazers (Archer et al. 1995,
Bahre 1995, Weltzin et al. 1997, Whitford 2002).
Historical conversion of desert grassland to desert
FIGURE 1. Ecosystems of the southwestern United States considered in this review.
STUDIES IN AVIAN BIOLOGY4 NO. 30
scrub has been nearly complete, and apparently
permanent, in many black grama grasslands at the
margins of the Chihuahuan desert (Schlesinger et al.
1990, Whitford 2002). However, recovery of native
desert grasslands can occur after long-term livestock
exclusion in relatively mesic areas (Valone et al.
2002), although it is not yet clear what role fi re might
play in this process (Valone and Kelt 1999).
FIRE EFFECTS IN CHIHUAHUAN DESERT SCRUB AND
DESERT GRASSLANDS
Birds associated with grasslands have declined
more than other avian groups, both nationally and
in the Southwest (Brown and Davis 1998, Vickery
and Herkert 2001) begging the questions: (1) What
have been the effects of contemporary fi res on veg-
etation and birds in desert grasslands, and (2) What
should be the role of prescribed burning in main-
tenance and restoration of southwestern grassland
bird habitats?
Fire can have two categorically different effects
on desert grassland vegetation and these in turn can
have very different effects on birds. In the short term,
fi re reduces grass cover for one to three post-fi re
growing seasons, while stimulating the abundance
and variety of forbs, and generally increasing seed
production (Bock et al. 1976, Bock and Bock 1978,
Bock and Bock 1992a, McPherson 1995). Results
of several studies in Arizona grasslands indicate
that these short-term effects can improve habitat for
seedeaters and open-ground species such as Scaled
Quail (Callipepla squamata), doves, Horned Larks,
and a variety of wintering sparrows (Table 1; Bock
and Bock 1978, Bock and Bock 1992b, Gordon
2000, Kirkpatrick et al. 2002). At the same time, fi re-
caused reductions of grass cover temporarily reduce
habitat quality for species dependent upon heavy
ground cover, such as Montezuma Quail (Cyrtonyx
montezuma), Cassin’s Sparrow, Botteri’s Sparrow,
and Grasshopper Sparrow (Table 1).
Over the longer term, fi re potentially can reduce
(but probably not eliminate) cover of woody vegeta-
tion in desert grassland communities, although fi re
effects on vegetation are species-specifi c and related
to season, grazing history, recent precipitation, and
fi re frequency (McPherson 1995, Valone and Kelt
1999, Drewa and Havstad 2001). Desert grasslands
that include mesquite and other woody plants usu-
ally support a higher abundance and species richness
of birds than open desert grasslands (Whitford 1997,
Lloyd et al. 1998, Pidgeon et al. 2001). However,
with the possible exception of the Cactus Wren
(Table 1; Kirkpatrick et al. 2002), these negative
effects have not yet been seen following fi re, prob-
ably because fi re frequencies and intensities have
been insuffi cient to result in much long-term loss of
woody cover.
Fire clearly had a historical importance in keep-
ing southwestern desert grasslands relatively free
of shrubs, but it has not yet been demonstrated
that prescribed burning can be used to restore these
conditions. This should be a high research priority.
Given the vulnerability of black grama to fi re in
the most arid sites, the major application of pre-
scription burning probably should be in relatively
mesic areas dominated by a variety of other native
perennial bunchgrasses. Some birds of the desert
grassland depend upon woody vegetation that is
a natural part of most Chihuahuan environments,
while others require relatively open areas with
substantial grass cover, and still others are attracted
to the bare ground and heavy seed crops that come
in the fi rst 2–3 yr after a burn. All of this argues
for maintaining a mosaic of landscapes in vari-
ous stages of postfi re succession, with some areas
unburned for decades and others burned perhaps on
a rotation of 3–5 yr.
In summary:
1. Prehistoric fi res probably were uncommon in the
Chihuahuan desert itself, but were important in
sustaining the surrounding desert grasslands, and
in determining the desert-grassland boundary.
2. Woody plants have increased in formerly open
desert grasslands, following introduction of live-
stock and resulting decreases in fi re frequency
and intensity.
3. Contemporary fi re in relatively mesic desert
grasslands has the effect of reducing grass cover,
while increasing bare ground, forb cover, and
seed production for 2-3 yr postfi re; over the lon-
ger term and with repeated burning, prescribed
fi re likely also could be used to reduce woody
vegetation and benefi t grasses.
4. Desert grassland and Chihuahuan desert avifau-
nas include some birds that depend on woody
vegetation, others that require heavy grass cover,
and still others that benefi t from open ground and
high seed production; the goal of prescription
burning should be to restore and sustain this sort
of habitat mosaic, with some areas rarely if ever
burned, and others burned on a 3–5 yr rotation.
5. A research priority should be to determine if
repeated fi re in desert grassland can reduce
woody vegetation to something resembling
prehistoric levels, and to better understand the
effects of such a fi re regime on the abundance
and demography of desert grassland birds.
SOUTHWESTERN UNITED STATES—Bock and Block 5
TA
BL
E 1
. S
UM
MA
RY
OF A
VA
ILA
BL
E L
ITE
RA
TU
RE O
N T
HE R
ES
PO
NS
E O
F B
RE
ED
ING
BIR
DS (
CH
AN
GE I
N A
BU
ND
AN
CE)
TO
FIR
E I
N S
OU
TH
WE
ST
ER
N H
AB
ITA
TS O
F N
OR
TH
AM
ER
ICA
.
Yea
rs
N
o.
afte
r S
ize
of
Res
p-
Type
Spec
ies
Sta
te
fi re
(h
a)
site
s onse
a of
fi re
R
efer
ence
b
Com
men
tsc
Sca
led Q
uai
l (C
all
ipep
la s
quam
ata
) A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
1-y
r in
crea
se
Monte
zum
a Q
uai
l (C
yrto
nyx
monte
zum
ae)
AZ
1–2
100,
150,
350
4
–
wil
d
1
saca
ton g
rass
land;
1-y
r dec
line
Shar
p-s
hin
ned
Haw
k (
Acc
ipit
er s
tria
tus)
A
Z
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Whit
e-w
inged
Dove
(Zen
aid
a a
siati
ca)
AZ
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land
; 1-y
r in
crea
se;
bre
edin
g s
easo
n
Mourn
ing D
ove
(Zen
aid
a m
acr
oura
) A
Z
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1, 3, 9, 20
350–2,8
90
4
+
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land
; 2-y
r in
crea
se
A
Z
1–2
1,5
96
14
+
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
A
Z
1–4
1,0
00
4
+
wil
d
5
mes
quit
e gra
ssla
nd;
1–3 y
r in
crea
se
A
Z
1–2
240, 120
4
+
wil
d
6
oak
sav
anna
Bro
ad-t
aile
d H
um
min
gbir
d
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n
(S
elasp
horu
s pla
tyce
rus)
Lew
is’s
Woodpec
ker
(M
elaner
pes
lew
is)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
resp
onse
to s
ever
e fi
re
Lad
der
-bac
ked
Woodpec
ker
A
Z
1n-2
1,5
96
14
+
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
(P
icoid
es s
cala
ris)
Hai
ry W
oodpec
ker
(P
icoid
es v
illo
sus)
A
Z
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; l
arger
incr
ease
foll
ow
ing s
ever
e fi
re
than
moder
ate
fi re
A
Z
7
10,0
00
14
+
wil
d
7
ponder
osa
pin
e; s
ame
area
as
above;
popula
tion i
n
sever
e fi
re a
reas
gre
ater
than
unburn
ed a
reas
, but
low
er t
han
that
rec
ord
ed a
fter
3 y
ears
A
Z
1, 3, 9, 20
350–2,8
90
4
+
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1
4,8
00
6
+
wil
d
8
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Nort
her
n F
lick
er (
Cola
pte
s aura
tus)
A
Z
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e
A
Z
1–2
100
6
–
pre
scr.
9
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Oli
ve-
sided
Fly
catc
her
(C
onto
pus
cooper
i) A
Z
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
resp
onse
to s
ever
e fi
re
Wes
tern
Wood-P
ewee
(C
onto
pus
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
posi
tiiv
e
so
rdid
ulu
s)
resp
onse
to s
ever
e an
d m
oder
ate
fi re
Ash
-thro
ated
Fly
catc
her
(M
yiarc
hus
N
M
14
6,2
50
4
–
wil
d
10
ponder
osa
pin
e; b
reed
ing s
easo
n
ci
ner
asc
ens)
A
Z
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
Log
ger
hea
d S
hri
ke
(Laniu
s lu
dovi
cianus)
A
Z
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd
Plu
mbeo
us
Vir
eo (
Vir
eo p
lum
beu
s)
AZ
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
neg
ativ
e re
sponse
to
sever
e fi
re
Ste
ller
’s J
ay (
Cya
noci
tta s
tell
eri)
A
Z
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e
A
Z
1, 3, 9, 20
350–2,8
90
4
+
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
STUDIES IN AVIAN BIOLOGY6 NO. 30
TA
BL
E 1
. C
ON
TIN
UE
D.
Yea
rs
N
o.
afte
r S
ize
of
Res
p-
Type
Spec
ies
Sta
te
fi re
(h
a)
site
s onse
a of
fi re
R
efer
ence
b
Com
men
tsc
Pin
yon J
ay (
Gym
norh
inus
cyanocp
ehalu
s) A
Z
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e
Cla
rk’s
Nutc
rack
er (
Nuci
fraga c
olu
mbia
na) A
Z
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e
Am
eric
an C
row
(C
orv
us
bra
chyr
hyn
chos)
AZ
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Com
mon R
aven
(C
orv
us
cora
x)
AZ
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e
Horn
ed L
ark (
Ere
moph
ila a
lpes
tris
) A
Z
1–4
10,0
00
4
+
wil
d
5
mes
quit
e gra
ssla
nd;
1–3 y
r in
crea
se
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
2nd y
r in
crea
se
Vio
let-
gre
en S
wal
low
(Tach
ycin
eta
AZ
1–2
100
6
–
pre
scr.
9
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
th
ala
ssin
a)
AZ
1
4,8
00
6
+
wil
d
8
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Mounta
in c
hic
kad
ee (
Poec
ile
gam
bel
i)
AZ
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; d
rast
ic d
ecli
ne
in s
ever
e burn
s
A
Z
1
10,0
00
14
–
wil
d
11
ponder
osa
pin
e; d
rast
ic d
ecli
ne
in s
ever
e burn
s
A
Z
1–2
100
6
+
pre
scr.
9
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
N
M
14
6,2
50
4
–
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Ver
din
(A
uri
paru
s fl
avi
ceps)
A
Z
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
Whit
e-bre
aste
d N
uth
atch
(Sit
ta
AZ
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; n
egat
ive
resp
onse
to s
ever
e fi
re
ca
roli
nen
sis)
A
Z
1
10,0
00
14
–
wil
d
11
ponder
osa
pin
e; n
egat
ive
resp
onse
to s
ever
e fi
re
A
Z
1
4,8
00
6
–
wil
d
8
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Pygm
y N
uth
atch
(Sit
ta p
ygm
aea
) A
Z
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; n
egat
ive
resp
onse
to s
ever
e fi
re
A
Z
1, 3, 9, 20
350–2,8
90
4
–
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
Bro
wn C
reep
er (
Cer
thia
am
eric
ana)
AZ
3
10,0
00
14
0/–
w
ild
2
ponder
osa
pin
e; n
o c
han
ge
in b
reed
ing s
easo
n;
dec
lines
in s
ever
e ar
eas
duri
ng n
onbre
edin
g s
easo
n
A
Z
1, 3, 9, 20
350–2,8
90
4
–
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
Cac
tus
Wre
n (
Cam
pyl
orh
ynch
us
A
Z
1–2
1,5
96
14
–
pre
scr.
4
mes
quit
e gra
ssla
nd
bru
nnei
capil
lus)
House
Wre
n (
Tro
glo
dyt
es a
edon)
NM
1
4
6,2
50
4
+
wil
d
12
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Ruby-c
row
ned
Kin
gle
t (R
egulu
s ca
lendula
) A
Z
1
4,8
00
6
–
wil
d
8
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
Wes
tern
Blu
ebir
d (
Sia
lia m
exic
ana)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; p
osi
tive
resp
onse
s to
sev
ere
and
moder
ate
fi re
s
A
Z
1
10,0
00
14
+
wil
d
11
ponder
osa
pin
e; p
osi
tive
resp
onse
s to
sev
ere
and
moder
ate
fi re
s
A
Z
1
4,8
00
6
+
wil
d
8
ponder
osa
pin
e; n
onbre
edin
g s
easo
n
N
M
14
6,2
50
4
+
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Her
mit
Thru
sh (
Cath
aru
s gutt
atu
s)
NM
14
6,2
00
4
–
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Am
eric
an R
obin
(T
urd
us
mig
rato
rius)
A
Z
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; p
osi
tive
resp
onse
s to
sev
ere
and
moder
ate
fi re
s
SOUTHWESTERN UNITED STATES—Bock and Block 7
TA
BL
E 1
. C
ON
TIN
UE
D.
Yea
rs
N
o.
afte
r S
ize
of
Res
p-
Type
Spec
ies
Sta
te
fi re
(h
a)
site
s onse
a of
fi re
R
efer
ence
b
Com
men
tsc
Nort
her
n M
ock
ingbir
d (
Mim
us
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
p
oly
glo
ttos)
Vir
gin
ia’s
War
ble
r (V
erm
ivora
vir
gin
iae)
N
M
14
6,2
00
4
–
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Lucy
’s W
arble
r (V
erm
ivora
luci
ae)
A
Z
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
Yel
low
-rum
ped
War
ble
r (D
endro
ica
AZ
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
neg
ativ
e re
sponse
to
co
ronata
)
se
ver
e fi
re
Gra
ce’s
War
ble
r (D
endro
ica g
raci
ae)
A
Z
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
avoid
ance
of
sever
e fi
re
A
Z
1, 3, 9, 20
350–2,8
90
4
–
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1, 3, 9, 20
350–2,8
90
1, 3, 9, 20
–
wil
d
13
ponder
osa
pin
e; b
reed
ing s
easo
n
N
M
14
6,2
50
4
–
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Com
mon Y
ello
wth
roat
(G
eoth
lypis
tri
chas)
AZ
1–2
150, 350, 100
4
–
wil
d
1
saca
ton g
rass
land;
2-y
r dec
line;
bre
edin
g s
easo
n
Wes
tern
Tan
ager
(P
iranga l
udovi
ciana)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
posi
tive
resp
onse
to
moder
ate
fi re
Gre
en-t
aile
d T
ow
hee
(P
ipil
o c
hlo
ruru
s)
AZ
1, 3, 9, 20
350–2,8
90
4
+
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
Spott
ed T
ow
hee
(P
ipil
o m
acu
latu
s)
NM
1
4
6,2
50
4
+
wil
d
10
ponder
osa
pin
e &
mix
ed-c
onif
er;
bre
edin
g s
easo
n
Can
yon T
ow
hee
(P
ipil
o f
usc
us)
A
Z
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
Cas
sin’s
Spar
row
(A
imophil
a c
ass
inii
) A
Z
1–2
1,5
96
14
–
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
A
Z
1–4
1,0
00
4
m
wil
d
5
mes
quit
e gra
ssla
nd;
2-y
r dec
line
in n
ativ
e gra
ssla
nd;
bre
edin
g s
easo
n
A
Z
1
? 6
–
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
A
Z
1–2
150, 350, 100
4
+
wil
d
1
saca
ton g
rass
land
; 2-y
r in
crea
se;
bre
edin
g s
easo
n
Bott
eri’
s S
par
row
(A
imophil
a b
ott
erii
) A
Z
1–2
1,5
96
14
–
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
A
Z
1–4
1,0
00
4
–
wil
d
5
mes
quit
e gra
ssla
nd;
2-y
r dec
line;
bre
edin
g s
easo
n
A
Z
1–2
100, 150, 350
4
–
wil
d
1
saca
ton g
rass
land
; 1-y
r dec
line;
bre
edin
g s
easo
n
Chip
pin
g S
par
row
(Spiz
ella
pass
erin
a)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1, 3, 9, 20
350–2,8
90
4
+
wil
d
3
ponder
osa
pin
e; b
reed
ing s
easo
n
A
Z
1–2
240, 120
4
+
wil
d
6
oak
sav
anna;
win
ter
Bre
wer
’s S
par
row
(Spiz
ella
bre
wer
i)
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
A
Z
1
? 6
0
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
Ves
per
Spar
row
(P
ooec
etes
gra
min
eus)
A
Z
1–2
1,5
96
14
+
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
A
Z
1–4
1,0
00
4
+
wil
d
5
mes
quit
e gra
ssla
nd;
2–3 y
r in
crea
se;
win
ter
A
Z
1
? 6
+
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
2-y
r in
crea
se;
win
ter
A
Z
1–2
240, 120
4
+
wil
d
6
oak
sav
anna;
win
ter
STUDIES IN AVIAN BIOLOGY8 NO. 30
TA
BL
E 1
. C
ON
TIN
UE
D.
Yea
rs
N
o.
afte
r S
ize
of
Res
p-
Type
Spec
ies
Sta
te
fi re
(h
a)
site
s onse
a of
fi re
R
efer
ence
b
Com
men
tsc
Lar
k S
par
row
(C
hondes
tes
gra
mm
acu
s)
AZ
1–4
1,0
00
4
+
wil
d
5
mes
quit
e gra
ssla
nd;
2-
yr
incr
ease
; bre
edin
g s
easo
n
Bla
ck-t
hro
ated
Spar
row
(A
mphis
piz
a
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd
b
ilin
eata
)
Sav
annah
Spar
row
(P
ass
ercu
lus
AZ
1–4
1,0
00
4
+
wil
d
5
mes
quit
e gra
ssla
nd;
1-y
r in
crea
se;
win
ter
s
andw
ichen
sis)
A
Z
1
? 6
+
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
2-y
r in
crea
se;
win
ter
Gra
sshopper
Spar
row
(A
mm
odra
mus
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
win
ter
sa
vannaru
m)
AZ
1–4
1,0
00
4
–
wil
d
5
mes
quit
e gra
ssla
nd;
2-y
r dec
line
A
Z
1
? 6
0
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
Bai
rd’s
Spar
row
(A
mm
odra
mus
bair
dii
) A
Z
1
? 6
0
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
Lin
coln
’s S
par
row
(M
elosp
iza l
inco
lnii
) A
Z
1
? 6
0
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
Whit
e-cr
ow
ned
Spar
row
(Z
onotr
ichia
A
Z
1
? 6
0
pre
scr.
14
mes
quit
e gra
ssla
nd;
win
ter
le
uco
phry
s)
AZ
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
1-y
r in
crea
se;
win
ter
A
Z
1
4,8
00
6
+
wil
d
8
ponder
osa
pin
e; w
inte
r
Dar
k-e
yed
Junco
(Ju
nco
hye
mali
s)
AZ
3
10,0
00
14
0
wil
d
2
ponder
osa
pin
e
Pyrr
hulo
xia
(C
ard
inali
s si
nuatu
s)
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
Blu
e G
rosb
eak (
Pass
erin
a c
aer
ule
a)
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd;
bre
edin
g s
easo
n
A
Z
1–2
100, 150, 350
4
–
wil
d
1
saca
ton g
rass
land;
2-y
r dec
line;
bre
edin
g s
easo
n
Eas
tern
Mea
dow
lark
(S
turn
ella
magna)
AZ
1–2
1,5
96
14
0
pre
scr.
4
mes
quit
e gra
ssla
nd
A
Z
1–4
1,0
00
4
m
wil
d
5
mes
quit
e gra
ssla
nd
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
2-y
r in
crea
se
Wes
tern
Mea
dow
lark
(Stu
rnel
la n
egle
cta)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n
Bro
wn-h
eaded
Cow
bir
d (
Molo
thru
s ate
r)
AZ
3
10,0
00
14
+
wil
d
2
ponder
osa
pin
e; b
reed
ing s
easo
n;
incr
ease
wit
h
moder
ate
fi re
House
Fin
ch (
Carp
odacu
s m
exic
anus)
A
Z
1–2
100, 150, 350
4
+
wil
d
1
saca
ton g
rass
land;
1-y
r in
crea
se
Red
Cro
ssbil
l (L
oxi
a c
urv
irost
ra)
AZ
3
10,0
00
14
–
wil
d
2
ponder
osa
pin
e; d
ecli
ne
wit
h s
ever
e an
d m
oder
ate
fi re
a C
han
ge i
n a
bu
nd
an
ce:
+ =
in
cre
ase
; –
= d
ecre
ase
; 0
= n
o e
ffect
or
stu
dy
in
co
nclu
siv
e;
m =
mix
ed
resp
on
se.
b R
efe
ren
ces:
1 =
Bo
ck
an
d B
ock
(1
97
8);
2 =
Bo
ck
an
d B
lock
(in
pre
ss);
3 =
Lo
we e
t al.
(1
97
8);
4 =
Kir
kp
atr
ick
et
al.
(2
00
2);
5 =
Bo
ck
an
d B
ock
(1
99
2b
); 6
= B
ock
et
al.
(1
97
6);
7 =
Blo
ck
an
d C
ov
ert
(u
np
ub
l. d
ata
); 8
= B
lak
e (
19
82
); 9
=
Ho
rto
n a
nd
Man
nan
(1
98
8);
10
= J
oh
nso
n a
nd
Wau
er
(19
96
); 1
1 =
Dw
yer
an
d B
lock
(2
00
0);
12
= J
oh
nso
n a
nd
Wau
er
(19
76
); 1
3 =
Ov
ert
urf
(1
97
9);
14
= G
ord
on
(2
00
0).
c U
nle
ss o
therw
ise i
nd
icate
d,
inclu
des
data
fro
m b
oth
bre
ed
ing
an
d n
on
bre
ed
ing
seaso
ns.
SOUTHWESTERN UNITED STATES—Bock and Block 9
SONORAN AND MOJAVE DESERT SCRUB
The Sonoran desert includes about 27,500,000
ha in the lowlands of southeastern California,
southwestern Arizona, most of Baja California,
and the western half of Sonora, Mexico (Robichaux
1999, MacMahon 2000). At its northwestern limits,
Sonoran desert grades into Mojave desert, which
includes another 14,000,000 ha of the lowest eleva-
tions in southeastern California, southern Nevada,
and northwestern Arizona (MacMahon 2000). These
deserts include species-rich, structurally complex,
and in many ways similar mixtures of shrubs, trees,
succulents, and annual forbs (Turner 1982, Turner et
al. 1995, MacMahon 2000). Dominant shrubs com-
mon to both deserts include creosote bush (Larrea
tridentata) and bur sage (Ambrosia dumosa).
Characteristic taller vegetation includes small trees
such as palo verde (Cercidium spp.) and columnar
cacti such as the saguaro (Cereus giganteus) in the
Sonoran Desert, and the Joshua tree (Yucca brevifo-
lia) in the Mojave desert.
The avifaunas of these deserts are species rich
compared to nearby desert grasslands (Tomoff
1974, Davis and Russell 1990), and they include
a variety of cavity-nesting species such as the Elf
Owl (Micrathene whitneyi), Ferruginous Pygmy-
Owl (Glaucidium brasilianum), Gila Woodpecker
(Melanerpes uropygialis), and Gilded Flicker
(Colaptes chrysoides) that depend upon large trees
and cacti for nest sites (Brown 1982a, Cartron and
Finch 2000, Hardy and Morrison 2001). At least in
the Sonoran Desert, there is a strong positive relation-
ship between vegetation volume and complexity, and
the overall abundance and diversity of birds (Tomoff
1974, Mills et al. 1991). Partners in Flight priority
species for one or both deserts include Gambel’s
Quail, Gilded Flicker, Gila Woodpecker, Costa’s
Hummingbird (Calypte costae), Cactus Wren,
Black-tailed Gnatcatcher (Polioptila melanura),
Rufous-winged Sparrow, and all four Southwestern
thrashers (Toxostoma bendirei, T. curvirostre, T.
crissale, and T. lecontei ).
FIRE IN SONORAN AND MOJAVE DESERT SCRUB
Wildfi res probably were relatively uncommon in
the Sonoran and Mojave deserts prehistorically, and
restricted to periods following wet winters, when
residual fi ne fuels left from annual forb production
were suffi cient to carry a burn across the otherwise
sparse desert fl oor (McLaughlin and Bowers 1982).
In the absence of dendrochronological data, Rogers
and Steele (1980) attempted to use degree of fi re
adaptation in perennial plants as evidence for his-
torical fi re frequency in the Sonoran desert. They
concluded that such adaptations were widespread
but relatively weak, and that a fi re-return interval of
anything less than 20 yr would be highly destructive
of most native trees, shrubs, and especially cacti (see
also McLaughlin and Bowers 1982).
The introduction and spread of exotic grasses
such as red brome (Bromus rubens) and buffelgrass
(Pennisetum ciliare), and a variety of exotic forbs,
increased both the frequency and intensity of fi re
in the Sonoran and Mojave deserts over the past
century, causing substantial mortality of woody
plants and succulents (Rogers 1985, Brown and
Minnich 1986, Schmid and Rogers 1988, Burgess
et al. 1991, Miller et al. 1995). Furthermore, both
seed and foliar production of these exotics are
likely to be enhanced by increased levels of carbon
dioxide, so that anticipated climate changes may
increase the frequency of fi re in these ecosystems
even beyond their present unnaturally high levels
(Smith et al. 2000).
FIRE EFFECTS IN SONORAN AND MOJAVE DESERT SCRUB
We could fi nd no studies that compared avian
species richness or abundance in burned versus
unburned Sonoran and Mojave desert landscapes.
However, there is little doubt that fi re-caused mor-
tality of desert woody plants and succulents would
have a strongly negative impact on the majority of
native bird populations, especially those dependent
upon trees and cacti for nest sites.
The principal management objective for Sonoran
and Mojave desert ecosystems should be to prevent
and suppress wildfi res that kill the native trees,
shrubs, and succulents. A critical research need is to
develop and test methods for limiting the spread and
abundance of exotic grasses and forbs responsible
for increased fuel loads. Cool-season, prescribed
burning is one possible method for reducing fuels,
but the risks are high because of the inherent fi re-
vulnerability of the native vegetation.
In summary:
1. Fires were historically uncommon in the Sonoran
and Mojave deserts, and much of the native veg-
etation is relatively intolerant of the effects of
burning.
2. Introduction and spread of exotic forbs and espe-
cially grasses have increased both the frequency
and intensity of fi re in these deserts, threatening
many of the shrubs, trees, and succulents that are
critical habitat components for birds.
3. The highest management and research priority
STUDIES IN AVIAN BIOLOGY10 NO. 30
is to fi nd ways of reducing the frequency and
intensity of wildfi re in Sonoran and Mojave des-
ert scrub habitats, by controlling the spread and
abundance of exotic forbs and grasses.
MADREAN EVERGREEN SAVANNA
This oak-dominated ecosystem includes about
1,500,000 ha of the Sierra Madre Occidental, largely
in Mexico, but extending north into southeastern
Arizona, southern New Mexico, and Trans-Pecos
Texas (D. E. Brown 1982, McPherson 1997).
Distributed mostly between 1,000 and 2,000 m
elevation, Madrean evergreen savanna grades into
desert grassland and mesquite savanna at its lower
elevational limits, and into pine-oak woodland at its
upper bounds. It is a typical savanna, with scattered
broad-crowned trees and a grassy understory. The
common oaks include Quercus emoryi, Q. arizonica,
and Q. grisea, frequently with scattered populations
of juniper (Juniperus deppeana, and J. monosperma),
and pinyon pine (Pinus cembroides).
Typical birds of southwestern oak savannas
include acorn-dependent species such as Acorn
Woodpecker (Melanerpes formicivorus) and
Mexican Jay (Aphelocoma ultramarina), foliage
gleaners and insect hawkers such as Bridled Titmouse
(Baeolophus wollweberi) and bluebirds (Sialia spp.),
and species dependent on the grassy understory such
as Montezuma Quail. Among these, the Montezuma
Quail, Mexican Jay, Bridled Titmouse, and Eastern
Bluebird (Sialia sialis) have been identifi ed as
Partners in Flight species of priority.
FIRE IN MADREAN EVERGREEN SAVANNA
Fire almost certainly maintained Madrean
evergreen savanna in a relatively open condition
prehistorically, favoring grasses over understory
shrubs and young trees (McPherson and Weltzin
2000). Cattle grazing and fi re suppression have
virtually eliminated wildfi re from an ecosystem
that probably evolved with a return interval of
about 10 yr (McPherson 1997). The result has
been a substantial increase in woody vegetation
at the expense of the understory grasses, over the
past century (Humphrey 1987, Turner et al. 2003).
There have been few studies examining the effects
of recent wildfi res or prescribed burns on this habi-
tat. Limited work suggests that the oaks can be top-
killed by fi re, but that they frequently resprout from
the lower trunk or root crown (Johnson et al. 1962,
Barton 1995).
FIRE EFFECTS IN MADREAN EVERGREEN SAVANNA
Two cool spring wildfi res in savannas at the
distributional limits of oak in southeastern Arizona
killed no mature trees, but they reduced grass cover
and increased forb cover and seed production for
two postfi re years (Bock et al. 1976). Total bird
abundance was greater on the burned areas, espe-
cially of winter seedeaters such as Mourning Dove
(Zenaida macroura), Vesper Sparrow (Pooecetes
gramineus), and Chipping Sparrow (Spizella passe-
rina). This result is generally consistent with those
from studies of wildfi re and prescribed burning
in mesquite grassland (Table 1). However, these
results tell us virtually nothing about the likely
responses of birds to hotter fi res that change wood-
land structure, and we found no other published
studies about fi re effects on birds in Madrean ever-
green savannas. In the midwestern United States,
fi res play a critical role in shaping the composition
of oak savannas and their avifaunas (Davis et al.
2000, Brawn et al. 2001). Fires in Madrean oak
savannas likely have similar effects, but they have
not yet been documented.
The goal of fi re management in Madrean ever-
green savannas should be to prevent stand-replace-
ment wildfi res that kill mature oaks to the ground,
since these events would eliminate a structural com-
ponent of the habitat that is critical for most of its
bird species. Cool-season, prescribed burning could
have the double benefi t of reducing fuels and the risk
of catastrophic wildfi re, and improving habitat for
birds such as the Montezuma Quail that depend on
dense understory grasses for escape cover (Brown
1982b). Determining avian responses to prescribed
understory fi re should be a research priority for
Madrean evergreen savanna.
In summary:
1. Wildfi re likely maintained oak-dominated
Madrean evergreen savanna in a relatively open
condition, with scattered broad-crowned trees
and grassy understory.
2. Fire suppression and fuel reductions caused by
livestock grazing have favored woody vegetation
over grasses.
3. The risk of catastrophic wildfi re has increased
historically, and birds dependent upon open
woodlands and grassy understory probably have
declined, although this has not been studied.
4. Cool-season prescribed burning could reduce the
risk of catastrophic wildfi re and improve habitat
for a variety of bird species in this habitat, but there
has been virtually no research on this subject.
SOUTHWESTERN UNITED STATES—Bock and Block 11
INTERIOR CHAPARRAL
North of Mexico, interior chaparral is best devel-
oped in a band south of the Mogollon Rim extending
from northwestern to east-central Arizona, where it
occupies about 1,400,000 ha (Pase and Brown 1982,
Keeley 2000). This shrubby habitat is more patchily
distributed to the south and east, across southeastern
Arizona, southern New Mexico, southwest Texas,
and onto the western slopes of the Sierra Madre
Oriental of northeastern Mexico, where it again
becomes a major vegetation type. Interior chaparral
is distributed from 1,000–2,000 m elevation in the
north, and from 2,000–3,000 m in the south. It usu-
ally intergrades with pine-oak woodland and with
grassland-desertscrub at its upper and lower eleva-
tional limits, respectively (Pase and Brown 1982,
Keeley 2000).
Interior chaparral consists primarily of a mix-
ture of dense perennial shrubs, especially live oak
(Quercus turbinella) and various species of manza-
nita (Arctostaphylos spp.) and Ceanothus (Keeley
2000). Some characteristic birds of interior chaparral
given priority status by Partners in Flight include
Crissal Thrasher (Toxostoma crissale), Virginia’s
Warbler (Vermivora virginiae), Green-tailed Towhee
(Pipilo chlorurus), Canyon Towhee (Pipilo fuscus),
and Black-chinned Sparrow (Spizella atrogularis).
FIRE IN INTERIOR CHAPARRAL
Fire-return interval for interior chaparral may
be 50–100 yr, much longer than that for the better-
studied California chaparral, and probably related
to its relatively low productivity (Keeley 2000).
Nevertheless, shrubs of interior chaparral recover
well from fi re, either by seed or by re-sprouting, and
post-fi re recovery may take only 5–10 yr (Pase and
Granfelt 1977, Carmichael et al. 1978). Drought,
livestock grazing, and suppression have reduced
fi re frequency over the past century, resulting in
increased shrub and reduced perennial grass cover in
Arizona interior chaparral (Brejda 1997). Research
and management have focused on effects of wildfi re,
prescription burning, grazing, and herbicide applica-
tion on attributes of chaparral ecosystems such as
livestock forage production, soil quality, and water-
shed function (Bolander 1981, Davis 1989, Overby
and Perry 1996, Brejda 1997).
FIRE EFFECTS IN INTERIOR CHAPARRAL
We found no published information on responses
of bird populations to fi re alone in interior chap-
arral. Szaro (1981) compared bird populations
between two stands of Arizona interior chaparral,
one unburned and un-manipulated for 20 yr, and the
other burned, treated with herbicides, and seeded
with exotic grasses. The avian assemblage in the
undisturbed chaparral was dominated by species such
as Gambel’s Quail, Mexican Jay (Aphelocoma ultra-
marina), Bewick’s Wren (Thryomanes bewickii),
Crissal Thrasher (Toxostoma crissale) , and Spotted
Towhee (Pipilo maculatus). The manipulated water-
shed supported only two common birds, the Rock
Wren (Salpinctes obsoletus) and Rufous-crowned
Sparrow (Aimophila rufi ceps). However, the herbi-
cide and seeding treatments doubtless obscured fi re
effects, so the results of this study cannot be taken as
indicative of avian responses to prescribed burning
alone. In studies of California chaparral, post-fi re
bird assemblages included higher proportions of
grassland species than those in unburned stands, but
the overall variety and abundance of birds were com-
parable (Lawrence 1966, Wirtz 1982).
Complete conversion of interior chaparral to
grassland, by whatever means, almost certainly
would negatively impact most birds. Prescribed
burning might benefi t birds and other wildlife in inte-
rior chaparral if it is used to create relatively small
openings in areas of heavy shrub growth, in order to
increase grass cover and habitat structural heteroge-
neity. This possibility should be tested, using a series
of replicated cool-season burns, matched with unma-
nipulated control sites, and sampled both before and
up to 5 yr after fi re.
In summary:
1. Wildfi re probably occurred prehistorically in
interior chaparral once every 50–100 yr, and
native shrubs are adapted to recover relatively
quickly; these fi res likely maintained patchiness
in this habitat, and facilitated development of
native grass cover.
2. Shrub cover has increased historically, as a result
of livestock grazing and fi re suppression, reduc-
ing habitat heterogeneity and increasing the like-
lihood of unnaturally large and intense wildfi res.
3. Prescribed burning might be used to reduce the
risk of wildfi re and to increase landscape het-
erogeneity benefi cial to chaparral birds, but this
possibility needs much more study.
PINYON-JUNIPER WOODLANDS
Pinyon-juniper woodland occurs throughout the
northern two-thirds of Arizona and New Mexico, an
area encompassing over 10,000,000 ha (Conner et al.
1990, Van Hooser et al. 1993). These woodlands are
STUDIES IN AVIAN BIOLOGY12 NO. 30
found between 1,200 and 2,700 m elevation and are
dominated by various pinyon pines (Pinus edulis, P.
discolor, and P. californiarum) and junipers (Juniperus
deppeana, J. osteosperma, J. monosperma, and J.
scopulorum). Tree species composition and structure
vary geographically and according to topography,
ranging from closed-canopy, mesic woodland to open
savanna (Moir and Carleton 1986).
Balda and Masters (1980) reported 73 bird spe-
cies that breed in pinyon-juniper woodland. Of these,
they concluded that 18 were highly dependent on this
habitat, including Western Screech-Owl (Otus ken-
nicotti), Black-chinned Hummingbird (Archilochus
alexandri), Ash-throated Flycatcher (Myiarchus cin-
erascens), Gray Flycatcher (Empidonax wrightii),
Western Scrub-Jay (Aphelocoma californica), Pinyon
Jay (Gymnorhinus cyanocephalus), Juniper Titmouse
(Baeolophus ridgwayi), Bushtit (Psaltriparus
minimus), Bewick’s Wren (Thryomanes bewickii),
Northern Mockingbird (Mimus polyglottos), Blue-
gray Gnatcatcher (Polioptila careulea), Gray Vireo
(Vireo vicinior), Black-throated Gray Warbler
(Dendroica nigrescens), House Finch (Carpodacus
mexicanus), Spotted Towhee, Canyon Towhee,
Lark Sparrow (Chondestes grammacus), and Black-
chinned Sparrow (Spizella atrogularis). Species of
concern within this ecosystem include Ferruginous
Hawk (Buteo regalis), Gray Flycatcher (Empidonax
wrightii), Pinyon Jay, Bendire’s Thrasher (Toxostoma
bendirei), Juniper Titmouse, Gray Vireo, and Black-
throated Gray Warbler.
FIRE IN PINYON-JUNIPER WOODLANDS
Historically, the primary role of fi re in pinyon-
juniper woodlands was more to limit its extent and
distribution, and to regulate tree densities, than to
change its composition or structure. This fi re regime
maintained large expanses of grassland, and grassy
openings within an open woodland. In addition to
regulating forest structure, fi re played important
roles in nutrient cycling, and in stimulating sprouting
and fruiting that led to increased food production,
especially for wintering populations of non-game
birds (Balda and Masters 1980). Grassland birds,
frugivores, and those that favored the interface
between woodland and grassland almost certainly
benefi ted from historical fi re regimes.
More recently, fi re suppression and the removal
of fi ne herbaceous fuels by grazing livestock have
facilitated expansion of pinyon-juniper woodlands
into formerly open grasslands, and led to increased
tree densities within existing woodlands (Pieper
and Wittie 1990). Concomitantly, the fi re regime
has changed from low-severity, stand-maintenance
burns to high-severity, stand-replacement burns.
Bird species most likely to be negatively affected
by this altered fi re regime are those that require live
trees for some aspect of their life history (O’Meara et
al. 1981, Sedgwick and Ryder 1987).
FIRE EFFECTS IN PINYON-JUNIPER WOODLANDS
Little information is available on fi re effects in
pinyon-juniper woodlands, particularly as related to
birds (Balda and Masters 1980, Pieper and Wittie
1990, Severson and Rinne 1990). Although the
ecological effects of chaining on bird habitats are
not equivalent to those of fi re, we consider effects
of chaining as they relate to tree removal. As one
would guess, species that depend on trees for forag-
ing or nesting, such as Black-throated Gray Warbler,
Plumbeous Vireo (Vireo plumbeus), White-breasted
Nuthatch (Sitta carolinensis), and Gray Flycatcher,
responded negatively to chaining (O’Meara et al.
1981, Sedgwick and Ryder 1987). Two species that
favor more open habitats, Rock Wren (Salpinctes
obsoletus) and Chipping Sparrow, appeared to
benefi t. However, we are reluctant to equate chain-
ing with burning. Chaining removes all standing
trees and snags, and reduces biomass and nutrients
in the system. In contrast, some trees and snags
remain standing following fi re. Residual snags, for
example, provide ephemeral (within 6 yr postfi re)
nesting substrates for cavity-nesting birds such as
Hairy Woodpecker (Picoides villosus) and Western
Bluebird (Sialia mexicana). As snags fall and are no
longer available as nesting substrates, populations of
cavity-nesting birds decline (Block, unpubl. data).
Fire also plays important roles in nutrient cycling,
and in stimulating sprouting and fruiting, which can
lead to increased food production, especially for
wintering populations of non-game birds (Balda and
Masters 1980).
Ideally, pinyon-juniper woodland should be man-
aged to restore ecosystem structure and function,
which would include returning to the historical fi re
regime. The practicality of doing so is dubious given
that it would entail concerted efforts to reduce both
grazing intensity and tree densities to provide condi-
tions needed to sustain low-severity, ground fi res.
Given the near absence of information on fi re
effects on birds in pinyon-juniper woodland, there
are numerous opportunities for research in this habi-
tat type. Priority, however, should be given to under-
standing how disruption of natural fi re regimes has
altered bird habitats and affected bird populations.
This research would focus on two general topics: (1)
SOUTHWESTERN UNITED STATES—Bock and Block 13
the habitat and population ecologies of birds in areas
that have lacked fi re for the past century, and (2)
the effects of recent large-scale, stand-replacement
fi res on bird habitats, populations, and communities.
Once these studies are completed, research experi-
ments should be conducted to elucidate effects of
potential management options to reduce fuels and
move toward conditions resulting from a more natu-
ral fi re regime.
In summary:
1. Fire once maintained pinyon-juniper woodlands
in a savanna-like condition, with numerous
grassy openings.
2. Fire suppression and loss of fuels to livestock
grazing reduced fi re frequency, resulting in
increased woodland density, and a shift to stand-
replacement fi res.
3. Almost nothing is known about bird responses to
fi re in pinyon-juniper woodland.
4. Research and management should focus on
understanding the ecology of birds in existing
unburned pinyon-juniper woodlands, on the
effects of recent stand-replacement fi res, and
eventually on ways to restore these woodlands to
their historic structural condition, including the
use of prescribed burning.
PONDEROSA PINE AND PINE-OAK
WOODLANDS
Southwestern montane forests include both
Cordilleran and Madrean fl ora. Cordilleran fl ora
dominates more northern latitudes, whereas Madrean
fl ora is largely restricted to basin-and-range moun-
tains in southeastern Arizona, southwestern New
Mexico, and along the Mogollon escarpment (Brown
1982a). The primary differences between the two
systems are the particular pine and oak species; the
overall structure is similar. Regardless of the fl ora,
woodland and forest vegetation generally occur in
gradients infl uenced by topography, aspect, soils,
and climate.
Ponderosa pine (Pinus ponderosa) is the most
common forest type in the Southwest, compris-
ing approximately 70% of the forested land base
(Conner et al. 1990, Van Hooser et al., 1993). At
lower elevations, ponderosa pine forest is bounded by
pinyon-juniper woodlands or oak savannas (Whitaker
and Niering 1964, 1965). These lower forests are
xerophytic, and ponderosa pine is the climax tree spe-
cies. Various pinyon pines (Pinus edulis, P. discolor,
P. californiarum), junipers (Juniperus deppeana, J.
osteosperma, J. monosperma, and J. scopulorum),
and oaks (Quercus grisea, Q. arizonica, Q. emoryi,
Q. hyperleucoides, Q gambelii, and Q. undulata)
occur as subdominant trees. Big sagebrush (Artemisia
tridentata), rabbitbrush (Chrysothamnus nauseosus),
and New Mexican locust (Robinia neomexicana) are
common shrubs, with blue grama (Bouteloua graci-
lis), Arizona fescue (Festuca arizonica), and moun-
tain muhly (Muhlenbergia montana) as the primary
grasses. With increasing elevation, ponderosa pine
forests become more mesophytic and, although still
the dominant tree, ponderosa pine is a seral species
amid mixed-conifer forests (Moir et al. 1997).
Hall et al. (1997) list over 100 bird species using
ponderosa pine forest. Some characteristic species
include Mourning Dove, Broad-tailed Hummingbird
(Selasphorus platycercus), Northern Flicker
(Colaptes auratus), Hairy Woodpecker, Western
Wood-Pewee (Contopus sordidulus), Violet-
green Swallow (Tachycineta thalassina), Steller’s
Jay, Common Raven (Corvus corax), Mountain
Chickadee (Popecile gambeli), White-breasted
Nuthatch, Pygmy Nuthatch (Sitta pygmaea), Western
Bluebird, Plumbeous Vireo, Yellow-rumped Warbler
(Dendroica coronata), Grace’s Warbler (Dendroica
graciae), Western Tanager (Piranga ludoviciana),
Red Crossbill (Loxia curvirostra), Cassin’s Finch
(Carpodacus cassinii), Pine Siskin (Carduelis
pinus), Chipping Sparrow, and Dark-eyed Junco
(Junco hyemalis). Bird species of special concern
within southwestern pine forests include Northern
Goshawk (Accipiter gentilis), Mexican Spotted Owl
(Strix occidentalis lucida), Flammulated Owl (Otus
fl ammeolus), Greater Pewee (Contopus pertinax),
Olive-sided Flycatcher (Empidonax (Contopus coo-
peri), Cordilleran Flycatcher (Empidonax occidenta-
lis), Purple Martin (Progne subris), Olive Warbler
(Peucedramus taeniatus), Virginia’s Warbler, and
Grace’s Warbler.
FIRE IN PONDEROSA PINE FORESTS AND PINE-OAK
WOODLANDS
Fire is perhaps the most important natural dis-
turbance in southwestern pine forests (Moir and
Dieterich 1988, Covington and Moore 1994, Moir
et al. 1997), and it infl uences plant composition, for-
est structure, and successional pathways. Frequent,
low-intensity fi res were part of the evolutionary
history of many lower-elevation forests, extending
up through mesophytic ponderosa pine and lower
elevation mixed-conifer (Savage and Swetnam 1990,
Moir et al. 1997). Crown fi res seldom occurred, and
they were confi ned to relatively small patches (Pyne
1996). Within the xerophytic pine, fi re occurred
every 2–12 yr and maintained an open grassy under-
STUDIES IN AVIAN BIOLOGY14 NO. 30
story and a patchy tree pattern. Given the frequency
at which fi res occurred, little wood debris accumu-
lated on the forest fl oor, and most fi re was fueled
by dead herbaceous vegetation. These low-intensity
fi res reduced understory fuel levels and killed small
trees, preserving the characteristic open stand struc-
ture (Cooper 1960, 1961; White 1985).
Within the past century, management and
economic activities, primarily fi re suppression,
livestock grazing, and logging, have had profound
effects, altering natural fi re disturbance regimes
and their effects on forest structure and composi-
tion (Cooper 1960, 1961, Covington and Moore
1994). The synergistic effects of these practices have
resulted in dense forests consisting mostly of small
trees, reductions in fi ne fuels, heavy accumulations
of ground and ladder fuels, and forests at high risk
of large-scale, stand-replacement fi res (Cooper 1960,
1961, Covington and Moore 1994). In addition, fi re
exclusion has led to changes in forest composition.
For example, lack of fi re has allowed shade-tolerant
fi rs (Abies spp.) to compete with dominant pines for
nutrients, thereby moving mesophytic pine forests
toward mixed-conifer forests (Moir et al. 1997).
Over-topping by pines has shaded out oaks and aspen
(Populus tremuloides), reducing their prevalence on
the landscape (Moir et al. 1997). In other areas, pines
are encroaching upon open meadows and parks,
converting them to forest (Moir et al. 1997). These
changes have combined to increase continuities of
fuels within and among stands, thereby increasing
the risk and prevalence of large-scale, stand-replace-
ment fi re (USDI 1995).
Given large-scale fi res of the past decade and
risks to lives and properties, land-management
agencies are beginning to implement fuels reduction
programs with the goal of abating fi re risk. Fuels
reduction includes tree thinning and prescribed fi re,
used singly or in combination. Little information
is available on the response of birds to such treat-
ments.
FIRE EFFECTS IN PONDEROSA PINE AND PINE-OAK
WOODLANDS
Generalizing fi re effects on birds in pine and
pine-oak forests is diffi cult, given differences in fi re
severity, intensity, and size, as well as the scale and
season of study. Short-term responses may differ
from long-term responses; breeding bird response
may differ from wintering bird response; and effects
observed at the stand scale may differ from those at
the landscape or regional scale. Lowe et al. (1978)
examined a series of fi res representing a chronose-
quence ranging from 1–20 yr postfi re, and found that
fi re effects changed with time (Table 1). Ground-for-
aging birds and woodpeckers increased immediately
following fi re, presumably in response to increased
food and nesting substrates, and then declined
once canopy cover began to recover and food sup-
plies diminished. Flycatchers reached their greatest
abundance about seven years following fi re, and then
decreased. Concomitant with population responses
might also be shifts in habitat-use patterns. Current
studies indicate that Hairy Woodpeckers occupy
smaller winter home ranges in forests 2 yr postfi re
than they use in forests 6 yr postfi re (Covert and
Block, unpubl. data). Presumably the amount of area
used corresponds to that needed for adequate food.
Populations of secondary cavity-nesting birds
responded differently to fi res of varying severities
in southwestern pine forests (Dwyer and Block
2000). Mountain Chickadee, Pygmy Nuthatch, and
White-breasted Nuthatch populations were lower 2
yr postfi re in areas of severe wildfi re, whereas only
the Mountain Chickadee declined in response to
moderate understory fi re. Western Bluebird popula-
tions were greater in severely burned forest than in
unburned forest. Dwyer (2000) also found that popu-
lations of Western Bluebirds increased in a severely
burned forest following introduction of nest boxes,
suggesting that nest cavities might be limiting after
fi re. This situation might change in time, once pri-
mary cavity-nesting species reestablish themselves.
In one of the few published studies of responses
by non-breeding birds, Blake (1982) found that, in
the year following a wildfi re, burned areas contained
more individuals but fewer species than unburned
areas. Some migrant and wintering species were
unique to burned areas during the fall, including
Common Poorwill (Phalaenoptilus nuttalli), Western
Wood-Pewee, Western Scrub-Jay, House Wren
(Troglodytes aedon), Hermit Thrush (Catharus gut-
tatus), and Lesser Goldfi nch (Carduelis psaltria).
Bird response to wildfi re varies by season and
fi re severity. Bock and Block (in press) present
data 3 yr post-wildfi re from an ongoing study in
northern Arizona (Table 1). Northern Flicker and
Hairy Woodpecker populations increased in both
moderately and severely burned areas, but increases
were greater in response to severe fi re. In contrast,
Broad-tailed Hummingbird, Western Wood-Pewee,
Plumbeous Vireo, and Western Tanager breeding
populations increased following moderate-sever-
ity fi re. When population declines were observed,
most were in response to severe fi re, including
Williamson’s Sapsucker (Sphyrapicus thyroideus;
nonbreeding), Steller’s Jay (breeding), Mountain
SOUTHWESTERN UNITED STATES—Bock and Block 15
Chickadee (breeding and nonbreeding), Brown
Creeper (nonbreeding), White-breasted Nuthatch
(breeding and nonbreeding), Pygmy Nuthatch
(breeding and nonbreeding), Plumbeous Vireo
(breeding), Yellow-rumped Warbler (breeding), and
Grace’s Warbler (breeding).
Most studies of fi re effects on birds in pine
systems have focused on stand-replacement burns.
These investigations provide little insight into the
probable effects of understory burning, or on avian
responses to habitat alterations associated with pre-
scribed fi re. Two studies are exceptions. Horton and
Mannan (1988) examined effects of prescribed fi re
on cavity-nesting birds in a pine-oak forest in the
Santa Catalina Mountains of Arizona. They sampled
birds prior to prescribed fi re, and then for one and
two years afterwards. They found few changes
in bird abundance, with Northern Flickers and
Violet-green Swallows decreasing, and Mountain
Chickadees (increasing. In the other study, Marshall
(1963) conducted a retrospective comparison of bird
communities within the Madrean Archipelago in
forests where natural fi re had occurred in Mexico,
versus similar forests north of the border where fi re
had been suppressed. He found that species com-
mon to brush or heavier forest cover, such as Ash-
throated Flycatcher, Black-throated Gray Warbler,
Scott’s Oriole (Icterus parisorum), and Spotted
Towhee were more abundant in the denser forests of
Arizona and New Mexico. In contrast, species typi-
cal of relatively open conditions, American Kestrel
(Falco sparverius), Cassin’s Kingbird (Tyrannus
vociferans), Purple Martin, Chipping Sparrow, and
Western and Eastern bluebirds, were more abundant
in Mexican forests.
Knowledge of the effects of wild and prescribed
fi re on birds is far less than what is needed to provide
a basis for management of southwestern ponderosa
pine forests. In particular, more studies are needed to
better understand effects of understory wildfi re and
prescribed fi re on birds. Meanwhile, we advocate
that fi re management strive to move toward histori-
cal fi re regimes, wherever possible. The most imme-
diate need is to reduce fuel continuity and the threats
of large, stand-replacing crown fi res. Research
should continue on ramifi cations of past manage-
ment so we have a basis for developing future man-
agement that ensures viable populations of species
native to Southwestern ponderosa pine forests. As
management options are developed, they should be
applied within an adaptive management framework
that monitors the response of bird populations and
communities to enable adjustments to management
through time.
In summary:
1. Wildifi re once maintained most southwestern
pine forests as relatively open stands, with large
scattered trees and a grassy understory.
2. The combined effects of fi re suppression, live-
stock grazing, and logging have caused most
southwestern pine forests to become crowded
by smaller trees, with a greatly-increased risk of
stand-replacement fi re.
3. The principal management objective for south-
western pine forests should be to return them to
their open condition, using prescribed fi re and
other methods, both to reduce their vulnerability
to catastrophic fi re and to enhance their habitat
value for birds and other wildlife.
4. Most research on avian responses to fi re in south-
western ponderosa pine forests has centered on
the results of high-intensity burns; future empha-
sis should be on results of low-intensity, ground
fi res that once characterized these forests, and
that will be an essential aspect of their future
management.
MIXED-CONIFER FORESTS
Mixed-conifer forests occur on approximately
20% of forested land in the Southwest (Conner at
al. 1990, Van Hooser et al. 1993). This represents
an increase since the 1960s, due in part to effects of
fi re suppression and the conversion of pine forest and
aspen stands to mixed conifer. The reduction of wild-
fi re disturbance in mesophytic ponderosa pine forests
favors shade-tolerant Douglas-fi r (Pseudotsuga men-
ziesii) and white fi r (Abies concolor) which become
the dominant tree species. Once this happens, the for-
est is more appropriately described as mixed conifer.
At lower elevations (2,000–2,400 m), mixed-
conifer stands are warm-climate forests dominated
by Douglas-fi r, white fi r, ponderosa pine, and
southwestern white pine (Pinus strobiformis), with
various broadleaf trees (e.g., Populus spp., Quercus
spp., Acer spp.) in the sub-canopy. At higher eleva-
tions (2,400–3,000 m), ponderosa pine is no longer
present, and mixed-conifer forests grade into spruce-
fi r forests consisting of Engelmann spruce (Picea
engelmanni), corkbark fi r (Abies lasiocarpa), white
fi r, and Douglas-fi r (Moir 1993). Trembling aspen
occurs as a seral species in most montane forest
types, where it can occur as a subdominant tree in
conifer forests, or as monotypic stands embedded
within a matrix of conifer forests.
Some birds characteristic of mixed-conifer in the
Southwest are Northern Goshawk, Mexican Spotted
Owl, Broad-tailed Hummingbird, Northern Flicker,
STUDIES IN AVIAN BIOLOGY16 NO. 30
Hairy Woodpecker, Williamson’s Sapsucker,
Cordilleran Flycatcher, Steller’s Jay, Mountain
Chickadee, Red-breasted Nuthatch (Sitta canaden-
sis), Golden-crowned Kinglet (Regulus satrapa),
Hermit Thrush, Plumbeous Vireo, Warbling Vireo
(Vireo gilvus), Yellow-rumped Warbler, Grace’s
Warbler, Olive Warbler, Red-faced Warbler
(Cardellina rubifrons), Dark-eyed Junco, and
Western Tanager. Birds of special management
concern include Northern Goshawk, the threatened
Mexican Spotted Owl, Williamson’s Sapsucker,
Olive-sided Flycatcher, Dusky Flycatcher
(Empidonax oberholseri), and Red-faced Warbler.
FIRE IN MIXED-CONIFER FORESTS
In lower elevation mixed-conifer forests, the
historical fi re regime was very similar to that occur-
ring in ponderosa pine, in that most events were
low-severity ground fi res (Grissino-Mayer et al.
1995, Moir et al. 1997). In contrast, many fi res that
occurred at higher elevations within mixed-conifer
and spruce-fi r forests were stand-replacing, provid-
ing opportunities for establishment of aspen. Since
it is a seral species, aspen will persist as long as
disturbance continues. In the absence of disturbance,
conifers will eventually overtop and outcompete
aspen for light and nutrients.
FIRE EFFECTS IN MIXED-CONIFER FORESTS
We found few studies from the Southwest that
specifi cally address the response of birds to fi re in
mixed-conifer forests. What little we can suggest
is extrapolated from studies in the Sierra Nevada
(Bock and Lynch 1970, Raphael et al. 1987) or
Rocky Mountains (Hutto 1995, Kotliar et al. 2002).
Certainly, fi re provides opportunities for a number
of species that occur in much lower numbers in
unburned forest. Bock and Lynch (1970) found
that 28% of 32 regularly breeding species occurred
only in burned forest, and 19% only in unburned
forest; overall, species richness was highest in the
burned forest. Species restricted to burned for-
est included Willamson’s Sapsucker, Olive-sided
Flycatcher, House Wren, Mountain Bluebird, Lazuli
Bunting (Passerina amoena), Green-tailed Towhee,
Chipping Sparrow, and Brewer’s Sparrow; those
restricted to unburned forest were Hermit Thrush,
Golden-crowned Kinglet, Plumbeous Vireo, and
Nashville Warbler (Vermivora rufi capilla).
Hutto (1995) identifi ed 15 species, primarily
woodpeckers, fl ycatchers, and seedeaters, that were
more abundant in post-fi re, mixed-conifer forest in
the Rocky Mountains. Of species mostly confi ned
to recent post-fi re conditions, four also occur in
the Southwest: Olive-sided Flycatcher, American
Three-toed Woodpecker (Picoides dorsalis), Clark’s
Nutcracker (Nucifraga columbiana), and Mountain
Bluebird (Sialia currucoides). Species found more
frequently in areas 10–40 yr postfi re included
Common Nighthawk (Chordeiles minor), Calliope
Hummingbird (Stellula calliope), Northern Flicker,
Orange-crowned Warbler (Vermivora celata), and
Chipping Sparrow. The American Robin, Yellow-
rumped Warbler, and Dark-eyed Junco were detected
in all early and mid-successional forest studies that
Hutto (1995) reviewed.
Kotliar et al. (2002) summarized results from 11
published and unpublished studies in conifer forests
of the western US, where severe, stand-replacement
wildfi re had occurred within 10 yr of data collec-
tion. Of these, only one (Johnson and Wauer 1996)
occurred in the Southwest. The studies occurred
in various forest types, although mixed-conifer
appeared best represented in their sample. Kotliar et
al. (2002) found that 9 of 41 species were more abun-
dant in recently burned forests, including American
Three-toed Woodpecker, Black-backed Woodpecker
(Picoides arcticus), Northern Flicker, Hairy
Woodpecker , Olive-sided Flycatcher, Mountain
Bluebird, Western Wood-Pewee, House Wren, and
Tree Swallow (Tachycineta bicolor). All of these
except the Black-backed Woodpecker are found
commonly in the Southwest.
Clearly, wildfi re in mixed-conifer forests cre-
ates habitats and provides resources that otherwise
would not be available for a variety of birds in these
ecosystems. However, not all species are favored by
fi re. Some, such as the Mexican Spotted Owl, require
older forests that result from years of fi re exclusion
(May and Gutiérrez 2002).
Following fi re, many mixed-confer forests transi-
tion into aspen. Given fi re suppression, aspen has
less opportunity to become established, and existing
stands succeed to mixed-conifer. Aspen forest is a
dwindling forest type in the Southwest that often
supports more species than surrounding conifer
forests, thereby contributing to greater landscape
diversity (Finch and Reynolds 1987, Griffi s 1999).
Management priorities should emphasize maintain-
ing and restoring aspen forests on the landscape.
More fi eld research specifi c to southwestern
conditions needs to be conducted to understand fi re
effects on birds in mixed-conifer forests. Clearly, the
various successional stages of mixed-conifer forests
support distinctive avifaunas, and thus all succces-
sional stages should be represented in appropriate
SOUTHWESTERN UNITED STATES—Bock and Block 17
quantities in the landscape (Kotliar et al. 2002).
This requires management that emulates natural fi re
regimes to the extent possible (Kotliar et al. 2002).
At lower elevations, this would require reducing lad-
der fuels and increasing fi ne fuels needed to carry
ground fi re. Potential tools to achieve these condi-
tions include reductions in grazing pressures, thin-
ning, and prescribed fi re.
At higher elevations, fi re management might
entail a combination of prescribed and natural
fi re, with well-planned fuel breaks consisting of
topographic or vegetation barriers that impede fi re
spread. Fire management at higher elevations is best
achieved with a mosaic of long-unburned stands
mixed with other areas that are burned with varying
frequencies and intensities. The resulting landscape
should possess the heterogeneity to provide habitat
for numerous species.
Future research should focus on the effects of
past management so we have a basis for ensuring
viable populations of species native to mixed-coni-
fer forests. As management options are developed,
they should be applied within an adaptive manage-
ment framework that monitors the response of bird
populations and communities to treatments, to
enable adjustments to management through time.
Research should be structured in such a way to
address questions at the appropriate scale in time
and space. Wildfi re in mixed-conifer forest results
in a shifting mosaic of seral stages through time.
To understand the dynamics of wildfi re, research
cannot be restricted to short-term studies but must
continue for decades. Similarly, research cannot
be restricted to small plots, but must be extended
to landscapes to better understand relationships at
the scale at which disturbance regimes manifest
themselves.
In summary:
1. Ground fi res once maintained low-elevation
southwestern mixed-conifer forests in a relatively
open condition, whereas higher-elevation forests
experienced stand-replacement burns that created
heterogeneous landscapes, including openings
for aspen regrowth.
2. Historical reductions in fi re frequencies caused
low-elevation forests to become dense, and all
southwestern mixed-confer forests to experience
occasional large stand-replacement fi res.
3. Few studies have been done of avian responses
to fi re in southwestern mixed-conifer forests;
however, studies in this habitat in the Sierra
Nevada and Rocky Mountains indicate that each
type of mixed-conifer forest supports a distinc-
tive avifauna, from unburned mature forests, to
aspen groves that follow stand-replacement fi res,
to open park-like forests maintained by ground
fi res.
4. Research goals should be to learn more about
habitat requirements of birds in southwestern
mixed-conifer forests, by conducting long-term
studies at appropriate landscape scales.
5. Management goals should be to return low eleva-
tion forests to the historic relatively open condi-
tion, and to create high-elevation mosaics of
unburned forests and those burned with varying
frequencies and intensities, especially including
those that provide opportunities for aspen.
RIPARIAN WOODLANDS
Riparian woodlands follow stream and river
channels that cross all the Southwestern ecosystems
discussed previously in this chapter. Dominant native
trees in southwestern riparian woodlands include
cottonwood (Populus spp.), sycamore (Platanus
wrightii), willow (Salix spp.), ash (Fraxinus velu-
tina), walnut (Juglans spp.), mesquite, and a variety
of others that can be locally common at different
elevations (Johnson and Jones 1977, Patten 1998,
Cartron et al. 2000).
Southwestern riparian woodlands support an
abundance and variety of breeding birds greater
than the relatively arid ecosystems adjacent to them.
Riparian avifaunas include some of the highest bird
densities ever reported, and many species that are
rare or missing elsewhere in the region (Carothers
et al. 1974, Strong and Bock 1990, Rosenberg et al.
1991, Nabhan 2000). Low and mid-elevation gallery
forests of large mature trees are particularly impor-
tant for both breeding and migratory birds (Bock
and Bock 1984, Szaro and Jakle 1985, Skagen et al.
1998, Powell and Steidl 2000). Riparian species that
appear most frequently on state and regional Partners
in Flight priority lists include Common Black-Hawk
(Buteogallus anthracinus), Yellow-billed Cuckoo
(Coccyzus americanus), Elegant Trogon (Trogon
elegans), Bell’s Vireo (Vireo bellii), Lucy’s Warbler,
and Abert’s Towhee (Pipilo aberti), along with
the endangered Southwestern Willow Flycatcher
(Empidonax trailii extimus; Sedgwick 2000).
FIRE IN RIPARIAN WOODLANDS
The frequencies and effects of prehistoric wild-
fi res in southwestern riparian woodlands are very
poorly understood (Dwire and Kauffman 2003).
While such fi res usually are assumed to have been
rare (Busch 1995), most riparian corridors cross
STUDIES IN AVIAN BIOLOGY18 NO. 30
upland ecosystems that burned relatively frequently,
and dominant native trees such as cottonwood and
willow have shown considerable ability to resprout
after fi re (Ellis 2001). Much more certain is that
the frequency and especially the intensity of fi res
have increased historically. While livestock graz-
ing may have reduced fuels somewhat, two other
factors have combined to make these ecosystems
more likely to experience intense fi re: the spread of
exotic saltcedar trees (Tamarix ramosissima); and
increasing aridity resulting from reduced fl ows and
altered fl ooding regimes (Busch and Smith 1995,
Ellis et al. 1998).
FIRE EFFECTS IN RIPARIAN WOODLANDS
We found no studies describing the response
of birds to fi re in southwestern riparian habitats.
However, we do not recommend prescribed burn-
ing as a research or management priority. Recent
fi res have been highly destructive of most native
riparian vegetation, while facilitating the spread of
saltcedar, which fails to provide habitat for many
native birds (Rosenberg et al. 1991, Busch 1995).
Research and management efforts should be directed
at fi nding ways to control saltcedar, and to restore
fl ow and fl ood patterns conducive to reproduction in
the native trees, especially cottonwood, willow, and
sycamore.
In summary:
1. Southwestern riparian woodlands support an
extraordinary variety and abundance of birds,
many of which have a high conservation prior-
ity.
2. Many of these ecosystems have been altered his-
torically by water impoundments and diversions
that reduce fl ows, change fl ood regimes, encour-
age the spread of exotic saltcedar, and increase
the frequency and intensity of fi re.
3. Research and management priorities should not
involve fi re, but should be directed at returning
fl ood regimes that favor native trees such as
cottonwood, willow, and sycamore that in turn
provide critical habitat for many Southwestern
birds.
RESEARCH AND MANAGEMENT
RECOMMENDATIONS
We have described habitat-specifi c research and
fi re management issues in the preceding sections
of this review. In summary, we do not recommend
application of prescribed fi re in Sonoran, Mojave,
Chihuahuan deserts, and associated xeric desert
grasslands, or in southwestern riparian woodlands.
Major threats to these ecosystems are the increased
fuel loads caused by invasions of exotic grasses and
trees, and the resulting increase in wildfi re frequency
and intensity. Managers and researchers must fi nd
ways to reverse these invasions, for the sake of
southwestern desert and riparian woodland ecosys-
tems and their associated avifaunas.
Wildfi re doubtless once played a highly signifi -
cant role in (1) sustaining mesic desert grasslands in
a relatively shrub-free state, (2) maintaining struc-
tural heterogeneity of interior chaparral, (3) limit-
ing the distribution and density of pinyon-juniper
woodland, (4) maintaining oak, pine, and low-eleva-
tion mixed-conifer ecosystems as open stands of
relatively mature trees, and (5) opening dense stands
of high-elevation, mixed-conifer forests and provid-
ing opportunities for aspen regrowth. Whenever
possible, prescribed fi re should be applied to mimic
these effects. This will have the double benefi t of
reducing fuels and the risks of large wildfi res, and
sustaining habitats upon which many southwestern
birds depend.
Successful implementation of prescribed burning
programs in southwestern ecosystems will not be
easy. In formerly open woodlands, such as pine and
oak, the challenge will be to keep fi re on the ground
where it can open the forest fl oor without harming
the mature trees. In higher-elevation mixed-conifer
forests, where stand-replacement fi res were a part of
the natural ecosystem dynamic, the challenge will be
to create landscapes with suffi cient fuel breaks so that
prescribed fi re can be contained in a desired area.
Finally, it is important to recognize that certain
kinds of birds require or prefer unburned areas,
even in ecosystems that have a long evolutionary
association with fi re. That is why burning all of any
particular landscape would be just as undesirable as
preventing fi re altogether. For every sparrow that
depends upon the seeds produced by recently burned
desert grassland, there is another that requires heavy
grass cover that a fi re temporarily destroys. For
every bluebird that prefers an open pine forest, there
is a towhee that does best where understory foliage is
dense. For every sapsucker that nests in fi re-depen-
dent aspen, there is a Mexican Spotted Owl that
prefers a mature stand of mixed-coniferous forest. In
all of these cases, the overall objective of manage-
ment must be to maintain landscape-level mosaics of
stands in various stages of postfi re ecological succes-
sion, including some areas long spared from fi re.
Given the prevalence and ecological importance
of fi re in the Southwest, there have been remarkably
few studies of the effects of fi re on southwestern
SOUTHWESTERN UNITED STATES—Bock and Block 19
birds, especially of prescribed burning and for eco-
systems other than ponderosa pine (Table 1). Also
scarce are studies about birds outside the breeding
season, or on demographic attributes other than
abundance, such as nesting success. Most of our
conclusions and recommendations about fi re and
birds in the Southwest are based on extrapolations
from known fi re effects on vegetation and gener-
ally understood habitat requirements of particular
bird species. We believe most of our conclusions
are reasonable, but they would be strengthened and
doubtless greatly refi ned by the results of more rep-
licated, large-scale, properly controlled fi eld stud-
ies. It always appears self-serving when scientists
call for more research, but in this case the need is
self-evident. Given increased public awareness and
concern about the destructive aspects of wildfi re in
the Southwest, there is a real danger that fi re preven-
tion and suppression policies will be implemented
that are as ecologically unfortunate as those of the
past century.
ACKNOWLEDGMENTS
We thank H. Powell, V. Saab, and two anony-
mous reviewers for helpful comments on an earlier
draft of this chapter.